1. Field of the Invention
The present invention relates to an indexing device in which a rotary member is rotated in steps by a predetermined angle for indexing thereof at a plurality of positions, and more particularly to such an indexing device which is suitably used as a tool indexing device, for example.
2. Prior Art
A known indexing device includes a rotary member, an axial drive mechanism, and a rotational drive mechanism. The rotary member is supported by a support member such that the rotary member is rotatable about its axis and axially movable between a first position and a second position. The axial drive mechanism operates to move the rotary member in an axial direction, while tee rotational drive mechanism having a one-way clutch operates to rotate the rotary member only in one direction (referred to as "forward direction"). In such an indexing device, the rotary member is rotated by the rotational drive mechanism in increments of a predetermined angle, after the rotary member is moved to the first position by the axial drive mechanism.
An example of such an indexing device in the form of a tool indexing device is disclosed in Publication No. 60-134536 of unexamined Japanese Utility Model Application. This tool indexing device has a body to which an adapter is attached such that the adapter is rotatable about its rotating axis and movable along the rotating axis between a retracted position and an advanced position. To the adapter, there is removably attached a tool holder which holds four cutting tools at equally spaced-apart angular positions of a circle having a center on the rotating axis of the adapter. While the adapter is fixed to the body in its retracted position, the tool indexing device performs cutting operations. Where one cutting tool is changed to another, the adapter is moved to its advanced position by the axial drive mechanism, and then rotated by the rotational drive mechanism by a predetermined incremental angle. The predetermined angle corresponds to a circumferential distance by which two adjacent cutting tools are spaced apart from each other. The rotational drive mechanism includes the one-way clutch so that the adapter is rotated only in the forward direction, whereby the four cutting tools are successively located in the operative position in order to perform the cutting operation on a workpiece.
In the above indexing device, since the rotation of the adapter in the forward direction with respect to the rotational drive mechanism is allowed by the one-way clutch, and there is provided no stopper means for inhibiting a further rotation of the adapter at a predetermined circumferential position, the adapter is rotated past the predetermined circumferential position due to inertia, whereby the appropriate cutting tool is displaced from the operative position. In this case, the circumferential position of the adapter can be adjusted by rotating the adapter such that the desired cutting tool is brought into the operative position. However, it is impossible to adjust the position of the adapter by rotating the same in the reverse direction, owing to the one-way clutch which permits the adapter to be rotated only in the forward direction. Therefore, it is necessary to rotate the adapter in the forward direction approximately by 360 degrees so as to adjust the circumferential position of the adapter. Such an adjustment is cumbersome and time-consuming.
Where the adapter is indexable at four circumferential positions by a positioning mechanism while being held in its retracted position, the positioning mechanism is inoperable when the adapter is rotated past a predetermined position, whereby the adapter cannot be restored to its retracted position.
The above indexing device suffers from another problem that it is difficult to fabricate the positioning mechanism for positioning the adapter when it is placed in its retracted position.
It has been proposed to provide a positioning mechanism which is constituted by two tapered grooves formed in the body of the indexing device and corresponding tapered keys provided on the adapter. The two tapered grooves intersect at right angles and each of the grooves has side walls which are spaced apart from each other by a distance which decreases toward the bottom of the groove. These tapered grooves and keys are difficult to form with high accuracy, resulting in increasing the cost of manufacture.
The above problems are not limited to the tool indexing device described above, but the same problems may be generally encountered in other types of indexing devices wherein the rotary member is rotated by a predetermined incremental angle, and indexed at a plurality of positions.